Method of coating foraminous metal with vitreous enamel



April 27, 1954 s. D. HACKLEY METHOD'OF COATING FORAMINOUS METAL WITH VITREOUS ENAMEL Filed A ril 4, 1951 FIG. I

FIG. 5

FIG. 6

a Y m MM 2 m A films bridging the openings. a wet suspension known as slip, the films, if

objects emb'odying'the invention.

Objectsmade in accordance withthe inven- Patented Apr. 27, 1954 UNITED STATES ATENT OFFICE METHOD OF COATING FORAMINOUS METAL WITH VITREOU S ENAMEL Sherlock D. Hackley, Pleasanton, Calif., assignor to Kaiser Metal Products, Inc., Bristol, Pa., a

corporation of California 6 Claims. 1

This invention relates to sheet material in fiat 'or shaped condition consisting of foraminous metal having a coating of vitreous enamel which covers the metal and extends across the interstices therein, forming a continuous vitreous enamel surface. Such material is useful for many purposes, since it is flexible, resistant to stains and discolorations, and easily cleaned, the surface being generally similar to that of vitreous enamel coated metal ware such as sinks and the like which are in common use. The product is, however, much lighter than enameled sheet metal ware because the metal base is non-continuous.

While the application of vitreous enamel to metal surfaces is well known, it has been generally accepted heretofore that such a coating could not be applied successfully to a foraminous metal base such as wire screening and sheet metal having openings therein because the vitreous enamel would not form suitable and permanent When applied in Another object of the invention is the provision of methods of producing such a'material.

Other objects and advantages of the inven-- tion will be apparent as it is better understood 'by reference to the following specification and accompanying drawing, in which Fig. 1 is an enlarged sectional view of the sheet material produced in accordance with my invention;

Fig. 2 is a plan view of the finished product;

Fig. 3 is a sectional .view of a shaped article of similar construction;

Fig. 4 is a diagrammatic view illustrating the procedure employed in making the product us ing a wet slip;

Fig. 5 is a view similar to Fig. 4 illustrating the method of applying enamel when the latter is melted prior to application to the foraminous base; and

Fig. 6 illustrates amethod of producing shaped tion as hereinafter described may have a metal base of wire mesh, the mesh varying from very small up to as large as 10 wires per inch approxi mately. Instead of wire mesh, foraminous metal produced by stamping, expanding or otherwise may be substituted. In carrying out the invention, the metal is coated and the interstices are filled by films of the enamel, which are supported between the coated wires or other metal surfaces forming a continuous vitreous enamel surface.

In order that the films may be formed and maintained in the interstices of the metal, it is necessary to employ an enamel material having the necessary viscosity and surface tension. In the ordinary practice of enameling metal surfaces, an aqueous slip is prepared by suspending a suitable frit, i. e., a powdered glass composition, in about 40% by weight of water. The slip is applied to the surface by spraying, dipping or otherwise, and then the material is dried to remove most of the water before firing. The slip as described is unsuitable for the present purpose because it lacks the necessary viscosity and surface tension. Moreover, I have discovered that if the product is dried before firing, the

,films are broken and a discontinuous surface results. The resulting product is a foraminous material which is useless for the purpose of the present invention.

The object of the invention can be accomplished, however, by preparing a slip containing only about 20% by weight of water. Such a ma terial is somewhat too viscous, and the viscosity is accordingly reduced by adding a suitable agent. Various agents are available for the purpose, for example citric acid or Abopon, a commercial product approximating the composition of sodium borophosphate, but I prefer to employ tetra sodium pyro phosphate in the proportion of approximately one part to 2,000 parts of dry enamel by weight.

This afiords a slip of the required viscosity and surface tension to form a coating and the films filling the interstices as desired.

The metal base may be coated with this mate- -'the enamel. There are numerous compositions of this character which are available and can be purchased ready for use, although additional grinding is often desirable in order to produce an entirely satisfactory vitreous enamel. I am unable to explain the somewhat unexpected result with reference to the elimination of the drying step, which has always been employed in the application of vitreous enamel. The reasons are obscure, but I have found that drying must be avoided in the application of vitreous enamel to foraminous metal, in order that continuous films bridging the interstices in the metal may be produced successfully.

Instead of employing a water-suspended frit or slip, the product may be made by dipping the foraminous metal in a molten frit. The material is subjected to heat until the glass is melted, and the foraminous metal is passed through or dipped in a bath of this material and permitted to drain and cool. Subseqi cut firing may or may not be required in this operation for control of surface or thickness of film.

Referring to the drawing, 5 indicates the wires forming the mesh of the metal screen material adapted to provide the base for the product. 6 indicates a coating of vitreous enamel covering the wires, and l, the films of vitreous enamel which extend between the wires, closing the interstices in the screen. It will be noted that the films 7 are somewhat less in thickness than the diameter of the wires 5, so that the surface of the material shows the characteri tic pattern of the screen base but nevertheless affords a continuous surface without openings, all of which are filled or bridged by the films This product is relatively flexible, that is to say, it can be bent through a considerable angle without breaking the vitreous enamel films. The surface has all of the desirable characteristics of vitreous enamel. It is impervious, is resistant to stains and discoloration, and is readily cleaned.

In Fig. 3, I have illustrated an object preformed of foraminous metal and subsequently coated with a vitreous enamel in accordance with the invention.

Referring to Fig. 4 of the drawing, I have illus-- trated diagrammatically a method of producing the product employing a wet slip. The foraminous metal 8 is withdrawn from a roll 9 thereof,

passed over and under guide rolls I5 and H,

through a bath of the aqueous slip in a container all. Here the foraminous metal receives a coating of the slip which covers the metal and bridges the interstices. The material then travels to a suitable furnace 53 which may be maintained at the desired temperature, for example by a gas burner it, to melt the glass composition of the slip, thereby fusing the material and forming a continuous surface of vitreous enamel covering the foraminous metal on both sides thereof. From the furnace l3, the material is withdrawn, passed over rollers 65 and [6 to permit sufiicient time for cooling, and then wound on a roll l1.

When the roll ii is of sufficient size, it may be from a roll l9, passed over and under guide rolls 20 and 2| through a molten bath of a suitable frit held in a container 22, which may be heated in any suitable manner, as for example by a gas burner 23. In passing through the container 22, the foraininous metal is coated With a molten frit, and films of this material are formed in the interstices. Subsequent firing of the enamel may or may not be used, depending upon the character of the frit employed. The coated material travels for a suflicient distance to ensure cooling and hardening of the vitreous enamel and may be directed by a guide roll 24 to the roll 25 where the material is wound for storage and shipment.

In Fig. 6, a preformed shape of foraminous metal 26; is carried on a conveyor 21 and dipped into a bath 28 of. aqueous slip or, if preferred, a molten frit. The conveyor 27 then carries the article through a furnace 29 if an aqueous slip is used. The furnace may be omitted if a fused frit is used.

As hereinbeforeindicated, various glass compositions suitable for the purpose of the present invention are readily available. Such compositions form no part of the resent invention. The following will serve as an example of a suitable material, it being understood that this composition is not intended to limit the invention, since other generally similar compositions may be sub stituted therefor.

Frit batch Materials Amount Feldspar 31 Borax 31 Quartz 20 Soda Ash 7 Soda Nitre 3 Fluorspar 6 Manganese Dioxide 1.5 Cobalt Oxide 0.5

Mill batch Materials Amount The above Prit 100.0

and

Clay 6 Water approx 20 Magnesium Carbonate 1% Silica 10 are mixed together and ground in a ball mill to required fineness to give a slip, which is thinned down by addition of small amount of tetra sodium pyrophosphate.

A frit batch composition. such as that described usually requires, when received at the plant, additional grinding to reduce the .par-

ticle size of the material which. has been produced by chilling a glass composition in water. After grinding to the desired size, the material is mixed with sufficient water to afford a slip of the desired viscosity. As already indicated. the preferred composition includes about 20% by weight of water, although this is subject to some variation. The slip should'not have anywhere near as much as 40 of Water by weight, since a 40% suspension of the material is too thin to afford films in the interstices of the metal which will stand up during the firing operation. If the slip containing only 20% of water is too viscous, the viscosity may be reduced by adding a suit able agent such as tetra sodium pyro phosphate in the relatively small amounts of approximately 1 part in 2000 by weight of the dry enamel. This will ensure the power viscosity and surface tension to provide films which ultimately produce the continuous surface, blocking out the interstices in the metal base.

Various changes may be made in the details of the operation as described without departing from the invention or sacrificing the advantages thereof.

I claim:

1. The method of producing a sheet of fo raminous metal covered with a continuous coating of vitreous enamel which comprises immersing the foraminous metal sheet in a vitreous enamel slip of fusible glass constituents and approximately 20%, by weight, of water, withdrawing the sheet with a coating of the slip material thereon, the foramens of the sheet being of such size that a continuous coating of the slip extends across each of the foramens of the withdrawn sheet and the thickness of the coating of the slip material in the foramens is such that, after fusing, it is of less thickness than the over-all thickness of the sheet, substantially immediately after the sheet has been withdrawn from the slip, and before the slip coating has become dry, subjecting the coated sheet to a sufficiently high temperature for a sufficient length of time to fuse the coating, and cooling the coated sheet while the coating still extends across the foramens thereof so that the film of material in all of the foramens remains continuous.

2. The method of claim 1 in which the slip contains a small amount of tetrasodium pyrophosphate.

3. The method of claim 1 in which the sheet of foraminous metal is wire mesh.

4. The method of producing a shaped article of foraminous metal covered with a continuous coating of vitreous enamel which comprises immersing the shaped article in a vitreous enamel slip of fusible glass constituents and approximately 20%, by weight, of water, withdrawing the sheet with a coating of the slip material thereon, the foramens of the shaped article being of such size that a continuous coating of the slip extends across each of the foramens of the withdrawn article and the thickness of the coating of the slip material in the foramens is such that, after fusing, it is of less thickness than the over-all thickness of the sheet, substantially immediately after the article has been withdrawn from the slip, and before the slip coating has become dry, subjecting the coated article to a sufficiently high temperature for a sufficient length of time to fuse the coating, and cooling the coated shaped article while the coating still extends across the foramens thereof so that the film of material in all of the foramens remains continuous.

5. The method of claim 4 in which the slip contains a small amount of tetrasodium pyrophosphate.

6. The method of claim 4 in which the shaped article is made of wire mesh.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 314,483 Scarles Mar. 24, 1885 1,221,562 Meyer Apr. 3, 1917 1,580,287 Colle et al. Apr. 13, 1926 1,783,738 McKeown Dec. 2, 1930 1,842,093 Haver Jan. 19, 1932 1,860,687 Moss May 31, 1932 2,113,370 Dunn et a1. Apr. 5, 1938 2,212,162 Littleton Aug. 20, 1940 2,475,469 Bennett et a1. July 5, 1949 2,527,884 Kauffmann Oct. 31, 1950 FOREIGN PATENTS Number Country Date 7,786 Great Britain of 1838 

1. THE METHOD OF PRODCING A SHEET OF FORAMINOUS METAL COVERED WITH A CONTINOUS COATING A VITREOUS ENAMEL WHICH COMPRISES IMMERSING THE FORAMINOUS METAL SHEET IN A VITREOUS ENAMEL SLIP OF FUSIBLE GLASS CONSTITUENTS AND APPROXIMATELY 20%, BY WEIGHT OF WATER, WITHDRAWING THE SHEET WITH A COATING OF THE SLIP MATERIAL THEREON, THE FORAMENS OF THE SHEET BEING OF SUCH SIZE THAT A CONTINUOUS COATING OF THE SLIP EXTENDS ACROSS EACH OF THE FORAMENS OF THE WITHDRAWN SHEET AND THE THICKNESS OF THE COATING OF THE SLIP MATERIAL IN THE FORAMENS IN SUCH THAT, AFTER FUSING, IT IS OF LESS THICKNESS THAN THE OVER-ALL THICKNESS OF THE SHEET, SUBSTANTIALLY IMMEDIATELY AFTER THE SHEET HAS BEEN WITHDRAWN FROM THE SLIP, AND BEFORE THE SLIP COATING HAS BECOME DRY, SUBJECTING THE COATED SHEET TO A SUFFICIENTLY HIGH TEMPERATURE FOR A SUFFICIENT LENGTH OF TIME TO FUSE THE COATING, AND COOLING THE COATED SHEET WHILE THE COATING STILL EXTENDS ACROSS THE FORAMENS THEREOF SO THAT THE FILM OF MATERIAL IN ALL OF THE FORAMENS REMAINS CONTINUOUS. 